arm64: dts: renesas: white-hawk-cpu: Add Ethernet support

Describe the wiring of the first Ethernet AVB instance to the Micrel
KSZ9031RNXVB PHY.

Based on a larger patch in the BSP by Takeshi Kihara.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/50a31bc8267ab4c90bff27ef3aca1169f8ebc7ae.1662715538.git.geert+renesas@glider.be

arch/arm64/boot/dts/renesas/r8a779g0-white-hawk-cpu.dtsi

@@ -16,6 +16,7 @@ / {
 	compatible = "renesas,white-hawk-cpu", "renesas,r8a779g0";
 
 	aliases {
+		ethernet0 = &avb0;
 		serial0 = &hscif0;
 	};
 
@@ -96,6 +97,24 @@ memory@600000000 {
 	};
 };
 
+&avb0 {
+	pinctrl-0 = <&avb0_pins>;
+	pinctrl-names = "default";
+	phy-handle = <&phy0>;
+	tx-internal-delay-ps = <2000>;
+	status = "okay";
+
+	phy0: ethernet-phy@0 {
+		compatible = "ethernet-phy-id0022.1622",
+			     "ethernet-phy-ieee802.3-c22";
+		rxc-skew-ps = <1500>;
+		reg = <0>;
+		interrupt-parent = <&gpio7>;
+		interrupts = <5 IRQ_TYPE_LEVEL_LOW>;
+		reset-gpios = <&gpio7 10 GPIO_ACTIVE_LOW>;
+	};
+};
+
 &extal_clk {
 	clock-frequency = <16666666>;
 };
@@ -127,6 +146,24 @@ &pfc {
 	pinctrl-0 = <&scif_clk_pins>;
 	pinctrl-names = "default";
 
+	avb0_pins: avb0 {
+		mux {
+			groups = "avb0_link", "avb0_mdio", "avb0_rgmii",
+				 "avb0_txcrefclk";
+			function = "avb0";
+		};
+
+		pins_mdio {
+			groups = "avb0_mdio";
+			drive-strength = <21>;
+		};
+
+		pins_mii {
+			groups = "avb0_rgmii";
+			drive-strength = <21>;
+		};
+
+	};
 	hscif0_pins: hscif0 {
 		groups = "hscif0_data";
 		function = "hscif0";